Vestibular imbalance is a serious problem due to loss of vestibular feedback resulted from various vestibular disorders. A vestibular rehabilitation therapy may alleviate the problem for some patients through regular training so that the brain can adapt to the vestibular loss with compensation from vision and proprioception. However, lost vestibular function cannot be fully compensated by visual and somatosensory cues, and the adaptation process may take months or years, and sometimes the adaption process may never be completed. Patients may become overly reliant on vision and proprioceptive senses, and postual instability often worsens when vision references are not reliable, or walking on uneven surfaces.
Various devices used to provide a prosthetic balance function may be implantable or non-implantable. The implantable stimulators are invasive and typically require surgical operations to be embedded under a patient's skin, such as within the ear canal in order to provide direct stimulation of the vestibular system.
Non-implantable prostheses are typically externally applied to the skin and thus are a much less invasive means of providing self-motion feedback. Such prostheses operate by, for example, stimulating the vestibular nerve via surface electrodes or by displaying self-motion cues using “sensory substitution,” for example by acoustic indications, vibrotactile feedback, or electric currents applied to the tongue.
Typically, tactile vibrators are mounted on the subject's torso. A vibrotactile system typically involves an array of small electromechanical vibrators distributed on the torso or mounted on the head.
Alternative sensory feedback is provided through electrotactile stimulation of the tongue. A tongue input device developed by Wicab Inc. consists of a popsicle-like electrode array placed inside the mouth and a controller hanging in front of the chest with a cable running in between.
With electrotactile stimulation of the tongue, cosmetic appearance is a big issue. Head movement and speech are restricted. Patients would rather use it for rehabilitative training in a private setting.
Relatively large but wearable motion sensing vestibular prostheses have been developed to fit around a person's torso. These are capable of providing a subject with information concerning tilt and sway in multiple axes and can be equipped with an “air bag” to deploy upon a user falling.